Ion exchange method

ABSTRACT

The invention is concerned with an ion exchange treating system wherein two or more exchanger or absorber vessels are connected in series, each vessel being filled with ion exchange resin leaving sufficient freeboard to allow for expansion of the medium. Each vessel is provided with an expansion chamber positioned above it and includes a conventional distribution system. The flow of liquids passing through the system is countercurrent with respect to the medium to be treated and the medium which regenerates the ion exchanger or absorber. Generally, the liquid to be treated enters the first vessel at the bottom, exiting from the top, entering the second vessel at the top and exiting therefrom at the bottom.

This is a continuation of application Ser. No. 544,712 filed Jan. 28,1975 which is a continuation of application Ser. No. 356,998 filed May3, 1973, both now abandoned.

This invention relates to the art of ion exchange adsorption andabsorbtion, and more particularly to ion exchange methods.

In the conventional ion exchange methods a pressure vessel is usuallyloaded with a stationary bed of ion exchange resin to a point where morethan about 50% of so-called freeboard is retained in the vessel. Thisfreeboard is normally required to allow expansion of the resin bedduring backwashing. In such a conventional process the process liquorspercolate through the bed of ion exchange resin, usually in the downflowfashion cocurrent between the alternating liquors.

It is also known that some installations alternate the liquors passingthrough the ion exchanger in a countercurrent flow pattern by allowing afluidized bed when proceeding upflow or by reducing flow to minimize bedfluidization. Other modifications in ion exchange methods and apparatusare known which attempt continuous operation rather than theconventional batch type system. The objective of all these modificationson the conventional ion exchange method and apparatus is to improveefficiency of operation.

Conventional ion exchange processes suffer one or more of the followingshortcomings which increase their investment and operating costs, andwhich may limit their application in many areas where it would be usedif these shortcomings could be eliminated:

1. Cocurrent flow or countercurrent flow through a partially fluidizedbed, respectively, of the alternating liquids which have to be passedthrough an ion exchange bed for exhaustion and regeneration,respectively, is inefficient. The ion exchange resin is only partiallyutilized and a large excess of regenerant must be applied to convert theion exchanger to the regenerated form under these conditions.

2. Because of the inefficient operation, the size of the plant must besubstantially larger than theoretically necessary.

3. Cocurrent flow compacts the resin bed and requires frequentbackwashings (1 - 2 backwashings per cycle). These backwashings requirelarge quantities of water which normally have to be disposed of, hencecreating also a disposal problem. Furthermore, backwashing represents asignificant portion of the total turn-around time, hence reducing thetime an ion exchanger may be used for actual exchange. This must betaken into consideration for plant design and results in significantlyenlarged investment cost.

4. The pressure drop through an ion exchange bed limits the height ofthe column and, hence, the amount of ion exchange resin that may beutilized in a single stream. Therefore, some installations with a largeflow to be treated require split stream operation, thus doublinginvestment cost. Such cycles are also relatively short, because of thelimited amount of resin which may be charged into a single vessel. Shortcycles dictate frequent interface fronts between dissimilar solutionspassing through the ion exchange column, hence causing dilution ofproduct and non-productive cycle lengthening because of lengthy rinsesand washings.

5. In the conventional ion exchange system, it is unavoidable to mixmake-up resin with resin which has already been degraded throughrepeated heavy use since it is economically not acceptable to replacethe whole lot of partially degraded ion exchange resin.

We have found that practice of the principles of the present inventiongreatly reduces the effects of the above shortcomings, thereby allowingimproved process efficiency, flexibility and ease of operation for anytype of ion exchange or absorbtion process, whilst at the same timeholding down investment costs.

The ion exchange apparatus for carrying out the present inventioncomprises one vessel, or, preferably two or more vessels, each of whichis filled with ion exchange resin or absorber, allowing only sufficientfreeboard for expansion of the resin bed due to normal swelling as theion exchange resin is converted from one form to another. Liquids areintroduced into or drained out of the resin bed, either from the top orfrom the bottom, respectively, through a distribution system which maytake any conventional form such as nozzles, screened radials, or evengravel bed support on the bottom, as long as proper consideration isgiven to uniform cross-sectional distribution of the liquid introducedor drained, respectively. Even a screened pipe opening will be operablewithin the scope of this invention, provided uniform cross-sectionaldistribution through the drainage system of the vessel containing theion exchange resin is not of significance. It is important, however,that the free openings of the inlet or outlet, respectively, to or fromthe vessel which are in contact with the ion exchange resin be of suchsize as to retain the latter within the vessel. The diameter of the ionexchange column is limited only by structural consideration. The heightof the column is limited by the pressure drop across the resin bed,which pressure drop depends upon the exchanger or absorber being used,the liquor being treated, and the respective flow rate of the liquor.

Two or more such vessels may be connected in series, with the liquid tobe treated entering Vessel No. 1 at the bottom, percolating upflow andexiting from the top of Vessel No. 1; thence entering the top of VesselNo. 2 to percolate downflow and draining out of the bottom of Vessel No.2. The flow may be taken to additional vessels in the same alternatingup and down flow pattern as explained for Vessels 1 and 2, with eachadditional vessel following this established flow pattern. For mostoperations only two such vessels need be connected in series forefficient operation, but the invention is not limited as to the numberof such vessels, columns, or cells connected in series.

Upon termination of percolation of the liquor to be treated, or when theion exchange resin or absorber is exhausted with respect to the chemicalspecies exchanged or absorbed, the regenerating medium may be passedthrough each respective vessel in a flow pattern countercurrent to thatof the liquor treated; e.g., entering the last vessel at a point wherethe treated liquor exited last.

It should be understood that the flow must not alternate up and downwith each additonal vessel, but the flow exiting from the top of VesselNo. 1 may be moved to the bottom of Vessel No. 2 for up-flowpercolation, hence providing consecutive upflow through each vessel forone type of liquor and consecutive but countercurrent downflow for theother type of liquid passing through the various vessels. It is also amatter of choice which of the liquors should flow only upflow and whichshould be arranged for downflow operation. However, the alternating upand down flow pattern explained first is the preferred choice for mostoperations, since it minimizes required pipe lines as well as havingother advantages. For a third variation of the countercurrent seriesflow, the vessels may be stacked on top of each other.

If required because of the nature of the substance to be treated via ionexchange such as viscosity, etc., or the number of vessels connected inseries for long exhaustion runs, respectively, it may be desirable toinstall in line booster pumps between vessels connected in series toavoid excessive pressures on the primary resin bed, - otherwiseunderstandably high pressures on the primary resin bed may be necessaryin order to maintain desirable flow rates in forcing the solutionthrough two or more vessels connected in series.

The alternating up and down flow combined with the countercurrent flowpattern of the various liquids passing through such a system result inobtaining the highest possible exchange efficiency either duringexhaustion or regeneration, respectively, and prevent compaction of theion exchange beds.

An outlet may be provided at the top of each vessel to allow connectionto an external non-pressurized expansion chamber. The top outlet mayrepresent between 0.3 % and 10 % of the total cross-sectional area ofthe vessel, and allows expansion of the resin bed into the expansionchamber located above the ion exchange vessel for the purpose ofbackwashing if such is desired. A single expansion chamber may beconnected to several ion exchange vessels. Preferably, no more than fourion exchange vessels arranged in cloverleaf formation should beconnected to one expansion chamber. However, each ion exchange vesselmay be connected to its own expansion chamber or a large expansionchamber my be compartmented accordingly. The expansion chamber may varyin size between one-half and two times the size of its respective ionexchange vessel, depending upon the type of ion exchange resin underconsideration and the expansion of the ion exchange resin desired. Theexpansion chamber should be equipped with an overflow; preferably aperipheral overflow or central downtake overflow, respectively.

The invention will now be further described in the following exposition,taken in conjunction with the appended drawing, in which

FIG. 1 is a schematic representation of an apparatus in the form for usein carrying out the product treatment step of the process of theinvention;

FIG. 2 shows the same apparatus as that in FIG. 1 but arranged to carryout the regeneration and rinse step;

FIG. 3 shows the same apparatus as arranged to carry out the backwashstep; and

FIG. 4 is a detailed view of the arrangement of radial distributors inthe ion exchange cell compartment of the apparatus.

In FIGS. 1-3 there are disclosed the basic components of one completeunit of apparatus for carrying out the process aspect of this invention,the same consisting of two associated similar assemblies. Each suchassembly includes an ion exchange cell 1 (or 1') provided with anexpansion chamber 2 (or 2') which cell and chamber communicate through avalve 10 (or 10'). The ion exchange cell is fitted with a bottom header3 (or 3') and associated assembly of radial diatributors 4 (or 4'), andalso with a top header 5 (or 5') and associated assembly of radialdistributors 6 (or 6'). A pipe 7 (or 7') leads from a source (not shown)to bottom header 3. At 9 (or 9') is indicated a drain controlled by avalve 8 (or 8').

Top headers 5, 5' are connected by a conduit 11, 11' in which there isintegrated an inline booster pump 12. A by-pass line 13, 13' leads from11 to 11' avoiding pump 12, said by-pass line including therein aby-pass valve 14.

Expansion chambers 2, 2' are equipped with overflow channels 20, 20'which overflow channels communicate through overflow conduit 21'.

Cells 1, 1' are, in use, filled with ion exchange resin bodies.

FIG. 4 illustrates a cross sectional view of screened radials. This is atypical form of an internal distributor system either upper or lowersuitable for the ion exchange cell.

In carrying out the product treatment and sweet off operation,exhaustant liquor is caused to traverse the unit via inlet pipe 7,bottom header 3 and its associated distributors 4 into and through abody of ion exchange resin filling cell 1; thence via upper distributors6, top header 5, conduit 11, 13, valve 14, conduit 13' and conduit 11',top headers 5' and associated distributors 6' into and through cell 1'(which, like cell 1, is filled with ion exchange resins), and exits fromthe unit via distributors 4', bottom header 31 and exit pipe 9'. In thisstep, valves 10, 10' as well as 8, 8', respectively, are closed.

If and when an undue pressure drop in pipe 11, 11' occurs, valve 14 isclosed and inline booster pump 12 is operated to induce a desired flowthrough the system.

In the succeeding regeneration and rinse operation (see FIG. 2)regenerant liquid traverses the unit, in reverse direction, viz., viapipe 7', header 3' and distributors 4' into and through cell 1, thecross-over communications, and into and through cell 1, exiting at exitpipe 7.

When backwashing is to be effected, valves 10, 10' are opened, andbackwash liquid is forced via bottom header 3, 3' and distributor 4, 4'through cells 1, 1' and valves 10, 10' and thence into expansionchambers 2, 2', overflowing at 20, 20' into overflow conduit 21 andthence to a recovery system if so desired.

The exchanger or absorber is allowed to drain back from the expansionchamber 2, 2' into cell 1, 1' after termination of backwashing bydraining liquid through distributor 4, 4', header 3, 3' and pipe 7, 7'.Valves 10, 10' are closed when the exchanger has settled back in cells1, 1'.

A valve and header system downstream from pipes 7, 7' controls thevarious liquid flows entering or exiting through pipes 7, 7' during thevarious operating steps.

Valves 8, 8' serve to drain the ion exchanger or absorber for inspectionof the cell interior, maintenance or replacement of the exchanger. Makeup of the exchanger is added via expansion chamber 2, 2' to enter thecell through valve 10, 10'.

We claim:
 1. A method for conducting an ion exchange operationcomprisinga. providing a system comprising at least two pressure vesselsconnected in series; each of said vessels containing a body ofparticulate ion exchange material substantially filling said vessel savefor sufficient freeboard to allow for the swelling of said exchangematerial during use; passage means proximate the lower and upper ends ofeach said vessel providing entrance and exit of fluid to be passedthrough said vessels whilst retaining within said vessels said bodies ofexchange material; each said vessel having a central opening in the topthereof; a non-pressurized expansion chamber located above said vesseland connected to said central opening to allow the entrance of saidexchange material from said vessel to said expansion chamber during backwash and drainage of said exchange material back into said vessel afterback wash, said central opening being provided with a valve whichcontrols communication between said vessel and said expansion chamber;said expansion chamber being provided with a down take overflow at itstop for discharge of back wash water; b. closing said valves in saidcentral openings, c. passing an exhaustant liquid into a first saidpressure vessel at the bottom thereof and upwardly through said body ofexchange material therein, said exhaustant liquid exiting from saidfirst pressure vessel at the top thereof; d. passing said exhaustantliquid to the top of a second pressure vessel and downwardly through thebody of exchange material therein, exiting at the bottom of said secondvessel, e. following the pattern so established for as many vessels asare connected in series; f. thereafter passing a regenerant liquid inthe aforesaid pattern counter current to the exhaustant liquid whichregenerant liquid enters at the point where the exhaustant liquid exitsand exits where the exhaustant liquid enters the system; g. opening saidvalves in said central openings; h. passing a back wash liquid into eachof said vessels at the bottom thereof and upwardly through said body ofexchange material therein, said back wash liquid exiting from each ofsaid vessels at the top thereof; i. passing said back wash liquidupwardly through said expansion chambers whereby causing said body ofexchange material to expand into said expansion chamber; j. passing saidback wash liquid upward through said expansion chambers to said downtake overflow where said back wash exits from said expansion chamber; k.terminating the flow of said back wash liquid to permit said body ofexchange material to settle back into said vessels; and l. repeatingsteps (b) through (k).
 2. The process as set forth in claim 1, whereinsaid expansion chamber comprises a single expansion chamber common toall of said vessels and said exchange material of said pressure vesselsexpand into said expansion chamber.
 3. The process as set forth in claim1, wherein said expansion chamber comprises a separate expansion chamberfor each of said vessels and said exchange material of each vesselexpands into its related expansion chamber.